In other eastern states, notably in the Baltics, there has been frustration with China's insistence that summit participants sign up to pre-cooked political declarations.
"Even though many announcements have been made and many cornerstones have been laid, there are very few tangible achievements, and even those are investments in the range of a few million dollars," Matura wrote in a December report on Chinese investments.
Late last month, German Chancellor Angela Merkel sent a veiled warning to EU states participating in Chinese government-led infrastructure projects, saying they should take care not to undermine the bloc's common foreign policy.
These countries have seen the summits as a way to lure Chinese investment in roads, railways, power stations and other infrastructure as part of Beijing's "Belt and Road" plan to build transport and trade links in more than 60 countries.
Enthusiasm remains strong in non-EU states like Serbia, which do not have access to EU structural or cohesion funds.
The diplomats said there were indications China could delay the next "16+1" summit, scheduled for the Bulgarian capital Sofia later this year, and hold future meetings every two years instead of on an annual basis.
"ONE EUROPE" On a visit to Berlin last month, Polish Prime Minister Mateusz Morawiecki said his country had greeted China's interest with "lots of enthusiasm" several years ago but did "not have too many good projects with China today".
Still, the Polish source described the summits as helpful and denied there was any talk about scrapping them. He suggested that "old Europe" countries like Germany were intent on weakening the format amid fears of growing Chinese influence.
ORBAN THREAT Besides China, the 16 countries that participate in the summits include EU members Bulgaria, Croatia, Czech Republic, Estonia, Hungary, Latvia, Lithuania, Poland, Romania, Slovakia and Slovenia, as well as non-EU states Albania, Bosnia and Herzegovina, Macedonia, Montenegro and Serbia.
The possible shift comes amid unease in Beijing over criticism of the summits in Brussels, Berlin and other capitals, at a time when the EU is discussing steps to more strictly control corporate takeovers of European firms by Chinese rivals.
Some capitals also complain about a lack of face time with Chinese leaders and Beijing's push for control of joint investment projects.
Her outgoing foreign minister, Sigmar Gabriel, irked China last year by calling on Beijing to follow a "One Europe" policy - a play on China's insistence that partners eschew diplomatic relations with self-ruled Taiwan, claimed by China as its own.
Hungary has also been a champion of the format. Prime Minister Viktor Orban said in January: "We need capital to build new roads and pipelines. If the EU is unable to provide enough capital, then we will simply collect it in China." Nevertheless, Tamas Matura, a professor at Corvinus University in Budapest, said the expected tsunami of Chinese investment into Hungary had not materialised.
At the urging of Germany, France and Italy, the EU is currently exploring the introduction of a mechanism to vet Chinese corporate takeovers in Europe - a move Beijing is lobbying aggressively to prevent.
"The 16+1 format won't die, because these formats never do, they have their own lives, but it will be a less intensive format, probably shifting more to bilateral talks," one senior EU official said.
BERLIN, BRUSSELS, SOFIA, REUTERS -- China is considering paring back annual summits with eastern European countries that have fuelled concerns in western capitals that Beijing is seeking to divide the continent, according to three European diplomats.
Another European diplomat suggested a decision had been taken at the highest levels of the Chinese government to lower the profile of the summits out of concern that they were hurting Beijing's image and undermining its broader goals in Europe.
Wider EU-China summits have become more tense in recent years, with the past two meetings failing to produce a joint statement amid disagreements over the South China Sea and trade.
"China realizes that the EU is not that comfortable," said the senior EU official. "China also realizes this is becoming a less popular format," he said of 16+1. "They don't like the bad press."
The Chinese foreign ministry did not respond to requests for comment. A spokesman for the Bulgarian government said Sofia was focused on its role as holder of the rotating EU presidency in the first half of 2018 and no date had been set for the next 16+1 summit.
"They say, we give you money, we control this," said a source close to the Polish government.
Some diplomats also cited disappointment in China and eastern Europe with the slow pace of deals under the format, which was launched in 2012 with a summit in Warsaw and has been held each year since, most recently in Budapest in November.